Anne Applebaum is a columnist for The Washington Post and the author of “Iron Curtain: The Crushing of Eastern Europe, 1944-1956.”

AFTER the shooting stopped in 1945, thousands of children and teenagers in Berlin’s ruins were left to their own devices. One in five schoolchildren had lost a parent. Despair gripped the adults in the capital, all of which was still under Soviet control.

In the western district of Neukölln, a group of young people decided to take matters into their own hands. Announcing on the day before the Allied victory that they would help rebuild the city, they formed a civic group and called it “anti-fascist.” Two weeks later, they had 600 members, had cleared the rubble from two sports stadiums and had organized five orphanages.

Inspired by their example, other young Germans began organizing similar anti-fascist groups in Berlin, but they didn’t last long. On July 31, the Soviet Military Administration banned all unregistered organizations. After that, many groups, clubs and associations were denied permission to exist....